The int scanf(const char *format, …) function reads the input from the standard input stream stdin and scans that input according to the format provided.
The int printf(const char *format, …) function writes the output to the standard output stream stdout and produces the output according to the format provided.
The format can be a simple constant string, but you can specify %s, %d, %c, %f, etc., to print or read strings, integer, character or float respectively. There are many other formatting options available which can be used based on requirements.
Example
#include <stdio.h> int main( ) { char str[100]; int i; printf( "Enter a value :"); scanf("%s %d", str, &i);/* &i is a pointer to variable i like str is a pointer to array str*/ printf( "\nYou entered: %s %d ", str, i); return 0; }
Note, that while reading a string, scanf() stops reading as soon as it encounters a space!!!
Usage of printf and scanf: %conversion character (d,i,u,o,x,…)
| %d, %i | int, decimal number |
| %u | int, unsigned decimal number |
| %o | int, octal number (unsigned), (without leading zero) |
| %x or %X | int, hexadecimal number (unsigned), (without leading 0x or 0X) |
| %c | int, single character |
| %s | char *, print characters from the string until a ‘/0’ or the number of characters given by the precision |
| %f | double; [-]m.dddddd, where the number of d’s is given by precision (default 6) |
| %e, %E | double; [-]m.dddddd e+/-xx or [-]m.dddddd e+/-XX, where the number of d’s is given by precision (default 6) |
| %g, %G | double, use %e or %E, if the exponent is less than -4 or greater than or equal than the precision; otherwise use %f. |
| %p | void *p; pointer |
| [-] | specifies the left adjustment of the argument |
| n | specifies the minimum field width |
| .n | number of digits after a decimal point or maximum number of characters to be printed from a string or minimum number of digits for integer |
An h if the integer is to be printed as a short and l if as a long (example %ld)
A width or precision may be specified as *, in which case value is computed by converting the next argument (must be int). For example, to print at most max characters from a string s: printf(“%.*s”, max, s);
For example: printf(“The result is: %-10.2f”, result); (left of the field, 10 characters with 2 decimals)
For example: scanf(“%d %s %d”, &day, monthname, &year); where monthname is an array and thus no & is needed, since an array name is already a pointer. The arguments to scanf must be pointers (like &day).
In the beginning of this lesson we copied input to output. Next we can make a program which count the characterics which the user enters.
#include <stdio.h>
/*Counting characters*/
main()
{
printf( “Enter a value and press Enter:\n“);
long number =0;
while(getchar() != ‘\n’)
++number;
printf(“%ld charateristics\n”, number);
}
Then one useful program more, a program which counts how many words the user have entered.
#include <stdio.h>
/*Counting words and characters*/
main()
#define IN 1 /*inside a word*/
#define OUT 0 /*outside a word*/
{
printf( “Enter a value and press Enter:\n”);
int number =0, words=0, input, state;
state = OUT;
while((input =getchar()) != ‘\n’)
{
++number;
if (input == ‘ ‘ || input == ‘\t’)
state = OUT;
else if (state == OUT)
{
state = IN;
++words;
}
}
printf(“%d charateristics and %d words\n”, number, words);
}